Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 170 of 707

ACID COPPER BATH CONSTITUENTS Figure 4: Tensile strength measured at 24°C and 35°C.. The developed process was formulated for high- volume rigid PWB pro- duction. A sulfate-based copper plating system that is well established for PWB fabrication was uti- lized. The method pre- sents low operational costs and is easy to con- trol. The development work goal was to achieve a process that is tempera- ture tolerant up to 40°C (104°F). The bath com- position, as well as the plating parameters, are given in Table 1. HT 100 Make-up is a mixture of wetter/sup- pressor that aims to improve start-up and Figure 5: Elongation measured at 24°C and 35°C. decrease dummy plating time for new baths. It is used only for new make- ups and after carbon treatments. HT 100 Brightener is responsible for copper grain refinement and internal stress reduction. It also has a leveling effect to smooth rough holes. HT 100 Wetter is a combination of organic additives that is used for replenishment during the plating process. TEST VEHICLES The test vehicle used in the process evaluation was 1.6-mm thick boards with var- ious-sized through-holes. The through-hole diameters were 0.2, 0.25, 0.35, and 0.5 mm. The process flow included the following operations: Acid cleaner: Wets the hole and removes light soils. Rinse Micro-etch: Etch undercuts and remaining debris to ensure excellent cop- per-to-copper adhesion. Rinse Acid dip: Acidifies copper surface prior to plating. The plating was performed at current densities of 1.0, 1.5, 2.0, 2.5, and 3.0 ASD. The solution temperature was in the range of 22–40°F. PROCESS FEATURES Surface Appearance. Fine-grained deposits were obtained from this electrolyte. Plated copper was smooth and leveled inside the hole. No thin copper at the knee of the holes was observed. In addition, no plating folds or thin areas inside the through-hole were measured. Plating thickness was consistent throughout the 169

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